Electromagnetic switches



April 2, 1963 H. REIFEL. 3,084,234

` ELECTROMAGNETIC SWITCHES Filed Aug. 15, 1960 2 Sheets-Sheet l Aprl 2, 1963 H. REIFEL ELECTROMAGNETIC SWITCHES 2 Sheets-Sheet 2 Filed Aug. 15, 1960 Unite This invention .relates to magnetic switches having cantilever-supported, vibratory, contact-actuating reeds.

Magnetic switches having cantilever-supported reeds of spring metal are widely used as choppers and relays. 'Such reeds are deiiected by magnetic fields set up by the iiow of current in associated coils, and usually bear contacts which touch, or actuate lContact lifters with contacts which touch, stationary contacts. The contacts are usually of a gold alloy for reducing the oxidation which occurs with copper contacts, and usually are -cylindrical in outline, with corresponding fixed and movable contact surfaces in general alignment when touching, although it has been proposed as disclosed in my U.S. Patent No. 2,878,337 which issued March 17, 1959, to use a wire as a movable contact, and to use another wire extending perpendicular to the movable wire, as a fixed contact.

A disadvantage of such prior contacts is that there is rubbing wear which after a period of operation, reduces the contacting areas, and increases the contact resistance, requiring early replacement.

This invention overcomes the disadvantages of such prior contacts by using a wire for one contact, and by using as the other cont-act, another wire extending perpendicular -to the one wire, and formed to have a wedgeshaped surface having a sharp edge at its apex where it contacts the yone wire. After a short, break-in period of operation, the sharp edge of one wire produces a wedgeshaped trough in the other wire, the sharp edge being deformed to a narrow, substantially flat surface, and the trough having -a correspondingly shaped bottom. This provides a large contact pressure with a small contact area.

It has previously been proposed to use a sharp point as one contact, and a flat surface as the other contact. The disadvantage of such a construction is that the point produces a round crater in the iiat surface, and ambient dust collects in the crater, reducing contact pressure and increasing contact resistance. The troughs produced in the movable contact Wires of this invention have converging ends, and any ambient dust collecting in the troughs is forced out their ends by the wedge-shaped contacts.

' An object of this invention is to increase the lives of contacts of magnetic switches.

Another object of this invention is to increase the contact pressure per unit of contact area of two co-operating contacts of la magnetic switch.

This invention Will now be described with reference to the annexed drawings, of which:

FIG. 1 is a plan view of a chopper embodying this invention, with a portion broken away, and another portion in section;

FIG. 2 is a side Per;

FIG. 3 is a perspective view of the contact making and breaking portion of a chopper similar to the one of FIG. 1 except that'its reed has no laminations;

FIG. v4 is an enlarged perspective view of one of the fixed contacts, showing its shape, and how it is attached to its contact plate;

FIGS. 5a and 5b are greatly enlarged, fragmentary, sectional views of a movable contact and its associated iixed contact respectively, showing the Icontact surfaces produced by a break-in period of operation, and

FIGS. 6a and 6b are enlarged fragmentary views of View on a reduced scale of the choparent the movable and fixed wires respectively, showing in plan the shapes of the contact surfaces produced by the break- A central brass, base plate 10 has side plates 11 of brass secured thereto by brass `screws 12. The base plate 10 has spaced-apart extensions 14 at one end (the left end of FIG. l) through which extends a screw 15 which clamps straps 16 onto the outside surfaces of the extensions 14, and which lhas a screw head 17 in contact with one tot the straps 16, and has a nut 18 in contact with the other strap.

Core 20 of an electromagnet 21 is clamped between the straps 16 at corresponding ends thereof, with a 10- cating pin 22 extending through the core 20 and the straps 16. Pole pieces 24 contact the ends of the core 20, and have extensions 26 bent through angles of 90, and which have spaced-apart ends 27. An electromagnetic shield 28 extends between the pole piece extensions 26 and the electro-magnet 21, and is supported by having one end clamped between one pole piece 24 and the adjacent plate 16. v

The center plate 10 has rectangular cut-outs 30 in the cor-ners of its opposite end, within which are supported brass blocks 31 which are clamped to the plate 10 by a bol-t 32 which extends through the blocks 31 and the central end portion of Vthe plate 10 between the cut-outs 30. Clamped between corresponding ends of the blocks 31y are insulators 34, brass spacers 35, the outer ends of brass plates 36, the outer ends of brass contact plates 37, brass spacers 38, insulators 39, brass spacers 40, the outer ends of brass contact litters 41 and the outer end of a brass reed 42.

The reed 42 has brass larninations 45 secured thereto on opposite sides thereof starting adjacent to where the reed is clamped and extending to the free end of the reed. The reed 42 at its free end has soft iron plates 46 riveted to opposite sides thereof, the free end of the reed and the corresponding ends of the iron plates terminating closely adjacent to the ends 27 of the pole piece extensions 26 of the electromagnet 21. The laminations 45 are .added to the reed for loading it so that it vibrates at a selected resonant frequency.

The center plate yl0 has a central recess 50 aligned with the space between the extensions 14 of the plate 10, and extending inwardly of the plate 10 to a location opposite the soft iron plates 46. A permanent magnet 57 extends within a transverse slot in the center plate 10 near the inner end of theslot 50. The magnet 51 rnagnetizes the iron plates 46 on the end of the reed so that they are intluenced by tield changes in the pole piece extensions 26 when A.C. is supplied to the electromagnet 21, and cause the reed to vibrate at the frequency of the applied A.C.

The inner ends `of the contact plates 37 have attached thereto and extending transversely thereof on their outer si-des, wedge-shaped contact w-ires 55 having sharp edges S6. As shown by FIG. 3, there are two, aligned, spacedapart, contact plates 37 on each side of the reed 42, having aligned contact wires 55. The wires 55 are attached to the contact plates as shown by FIG. 4. A transverse recess 57 is formed across each plate 37, the recess being triangular in section. A wire 55 which is round at the time of installation, is placed in the recess, the wire being larger than the recess so that its rnajor portion protrudes from the recess. The portion of the wire within the recess is spot welded to the plate 37, and the portion of the wire which protrudes from the recess is ground away to the wedge shape shown by the drawings, with a sharp edge 56 at its apex.

The outer side of the :inner end of each contact lifter 41 has spot welded thereto, the outer end of one leg 59 of a U-shaped contact Wire 60 which straddles the outer end of its associated contact plate ,37, and which has its other leg 61 opposite the sharp edge 56 of its associated contact wire 55. The edge 56 Iof a wire 55, and the axis of its associated contact wire leg- 61 extend in planes which are perpendicular to eachother.

` The plates 36 have small lbolts 70 threaded therein, and the'inner ends of which touch the outer sides of the contact lifters 36, and' which are used for adjusting the spacings between thecontaot wires 55 and 61.

FIG. 2` shows one'electromagnet 21, and one reed and contact assembly on onel side of a center plate 10, and itsk side plates 11. Another electromagnet and another reed -and contact assembly couldV `be supported on the' other side of the center and side plates for .combining two choppers in one over-all assembly.

In operation, A.C. applied to the coil of the electromagnet 21, produces a varying magnetic iield between the ends 27 or the pole piece extensions 26, which cause the iron plates 46 on the free end of the reed 42, which plates a'r'e magnetize-d by the permanent magnet 51, toV vibrate the reed. Movement of the reed in one direction from its normal central position, causes it to move the contact lifters 41 in contact with one of its sides in that direction to force the sharp edges of their contact wires 55 against the associated contact wires 61 for closing an external circuit in which such contact wires are con`` nected. When the reed is moved in the opposite direction, the contact litters which were moved by the reed when the latter moved in the one direction, return to their normal position inr which their contact wires 55 are spaced from their associated contact wires 61, and the contact lifters 41 in contact with the opposite side of the reed are moved in the opposite direction so that their contact wires 55 are forcedagainst their associated contact wires 61 for closing another external circuit in which such conta-ct wires are connected.

The two-parallel-connected contact wires 55, and the two'parallel-connected wires 61 .on each side of the reed are provided as` a factor of safety in case of damage to one set ofrc'ontact wires.4

The illustrated contact wires are of a `gold alloy. As shown in exaggerated fashion by FIG. 5b, the sharp edge 56" of a wedgeshaped `contact Wire 55 is deformed after ashort, 'break-in peniod of operation, so that the apex of the wedge where .it contacts the Wire 61, becomes a narrow, substantially iiat surface 75. As shown by FIG. S, a wedge-shaped trough 76 having a narrow, subs'tantially flat bottom 77 is formed during the break-in period, in and transversely of the wire 61 where it contacts the Wire 55. The trough 76 has converging ends as shown by FIG. 6a, -and any dust which would tend to collect in the trough would be forced out its ends when the flat surface 75 of the contact wire 55 is forced through the Vdust against the bottom of the trough.

'I'he described break-in operation is performed at the factory so that when a chopper is shipped to a customer, it has contact wires with the troughs, and contact wires with narrow flat surfaces at the apices of'wcdge-s-haped portions as described in the foregoing. The metal of the wires is compressed during the break-in period that no further significant deformation can take place during the service operation.

What is claimed, is:

1. In an electromagnetic switch having a' cantileversupported reed of spring metal, and having means for vibrating said reed, the improvement comprising a contact wire containing precious metal movable with said reed,-a fixed contact wire containing precious metal, said wires having longitudinal axes extending in mutually perpendicular planes, one of said wires having a wedgeshaped portion having an apex formed as a narrow, substant-ially flat surface, and ltheI other of said Wires having a wedge-shaped trough with converging ends and a narrow, substantially flat -bottom opposite and normally spaced from said surface.

2. In an electromagnetic switch having a cantileversupported reed of spring metal, and having means for vibrating said reed, the improvement comprising a contact lifter movable with said reed, a contact wire containing precious metal attached to said lifter, and a fixed contact wire containing precious metal normally spaced from said iirst mentioned wire, said wires having longitudinal axes extending lin mutually perpendicular planes, one of said` Wires having a wedge-shaped portion having an apex formed as a narrow, substantially hat surface, and `the other of said wires having a Wedge-shaped trough withy converging ends and a narrow, substantially flat bottom opposite and normally spaced from saidl surface.

3. In an electromagnetic switch having a cantileverlsupported reed of spring metal, and having` means for vibrating said reed, the improvement comprising a contact wire containing precious metal movable with saidreed, a iixed contact plate having a transversely extending recess, a iixed contact wire containing precious metal having a rounded portion in said recess, and having a wedge-shaped portion extending outwardly from said plate, the apex of said Wedge-shaped portion -being formed `as a narrow, substantially at surface, said wires having longitudinal axes extending in mutually perpendicular planes, said first mentioned wire having a wedge-shaped trough with converging ends and a narrow, substantially at bottom opposite and normally spaced from said surface.

4. In an electromagnetic switch having a reed of spring metal, having means for supporting one end of said reed, and having means for vibrating said reed, the improvement comprising a contact lifter movable With said reed, and having one end supported by said supporting means, a contact plate having Vone end supported by said supporting means insulated from said reed and lifter, said plate having attached thereto and extending transverselythereof a contact wire containingprecious metal having a wedge-shaped portion extending from said plate, said wedge-shaped portion having an apex formed as a, narrow, substantially at surface, a U-shaped contact wire containing precious metal straddling the other end of said contact plate with one leg attached to said lifter and the other Yleg `having a wedge-shaped trough with converging ends and a narrow, substantially flat bottom opposite and normally spaced from said surface, the longitudinal axes of said rst mentioned wire and of said other leg extending -in mutually perpendicular planes.

5. The invention claimed in claim 4in which saidplate has a wedge-shaped recess, and in which said rst mentioned wire has a'rounded-portion opposite said flat surface in said recess.

References Cited in the le of this patent UNITED STATES PATENTS 

1. IN AN ELECTROMAGNETIC SWITCH HAVING A CANTILEVERSUPPORTED REED OF SPRING METAL, AND HAVING MEANS FOR VIBRATING SAID REED, THE IMPROVEMENT COMPRISING A CONTACT WIRE CONTAINING PRECIOUS METAL MOVABLE WITH SAID REED, A FIXED CONTACT WIRE CONTAINING PRECIOUS METAL, SAID WIRES HAVING LONGITUDINAL AXES EXTENDING IN MUTUALLY PERPENDICULAR PLANES, ONE OF SAID WIRES HAVING A WEDGESHAPED PORTION HAVING AN APEX FORMED AS A NARROW, SUBSTANTIALLY FLAT SURFACE, AND THE OTHER OF SAID WIRES HAVING A WEDGE-SHAPED TROUGH WITH CONVERGING ENDS AND A NARROW, SUBSTANTIALLY FLAT BOTTOM OPPOSITE AND NORMALLY SPACED FROM SAID SURFACE. 